Conventional OCT generates one or few cross-sections of the retina and requires predetermination of measurement location and geometry. Because retinal pathologies are usually irregular and 3-dimensional in nature, a retinal imaging device with both high depth resolution and high lateral resolution is desired. The lateral resolution of the conventional OCT system is limited by sampling density, which in turn is limited by the speed of the system. In this paper, we present a three-dimensional optical coherence retinal tomograph (3D-OCT) which combines the rapid transversal imaging mode of a confocal scanning laser ophthalmoscope (cSLO) with the depth resolution of optical coherence tomography (OCT) to achieve high speed 3-D imaging. In contrary to the conventional OCT which performs adjacent A-scans to form a cross-section image (B-scan) perpendicular to the retinal surface, 3D-OCT acquires section images (C-scan) parallel to the retinal surface at defined depths across the thickness of the retina. Three-dimensional distribution of light-remitting sites within the retina is recorded at a depth resolution of ~12 μm (in eye) and lateral resolution of 10μm x 20μm within 1.2 seconds. In this paper, we present the results of in vivo retinal imaging of healthy volunteers and diabetic patients, retinal thickness mapping, and macular edema detection with the 3D-OCT device. Reproducibility of retinal thickness mapping ranges from 16 μm ~ 35 μm for different study subjects. Detailed retinal thickness map allows ready identification of location and area of macular thickening. C-scan images and continuous longitudinal cross section images provide visualization of pathological changes in the retina, such as presence of cyst formation and hard exudates. The need to predetermine measurement location and geometry is eliminated in 3D-OCT, in contrast to conventional OCT.
KEYWORDS: Optical coherence tomography, Retina, 3D image processing, Head, 3D scanning, In vivo imaging, Prototyping, Optic nerve, Image resolution, Nerve
Most of the presently used OCT systems are based on A-scans, i.e., the fast scanning direction is the z-direction. We have developed a new OCT technique for retinal imaging that is based on a transversal scanning scheme and combines the imaging modes of a scanning laser ophthalmoscope with the depth sectioning capability of OCT. A stable high-frequency carrier is generated by use of an acousto optic modulator, and high frame rate is obtained by using a resonant scanning mirror for the priority scan (x-direction). Our prototype instrument records 64 transverse images consisting of 256x128 pixels in 1.2 seconds, thus providing the fastest retinal 3D OCT time domain scanning system reported so far. We demonstrate the capabilities of our system by measuring and imaging the fovea and the optic nerve head region of healthy human volunteers in vivo.
Qienyuan Zhou, Jerry Reed, Ryan Betts, Peter Trost, Pak-Wai Lo, Charles Wallace, Richard Bienias, Guoqiang Li, Ross Winnick, William Papworth, Michael Sinai
One of the earliest signs of glaucoma presence is defects in the retinal nerve fiber layer (RNFL). Scanning laser polarimetry (SLP) provides objective assessment of RNFL, a birefringent tissue, by measuring the total retardation in the reflected light. SLP provides a potential tool for early detection of glaucoma and its progression. The birefringence of the anterior segment of the eye, mainly the cornea, is a confounding variable to SLP's clinical application, if compensation cannot be achieved properly. This paper presents a new SLP system, GDx VCC (Laser Diagnostic Technologies, Inc., San Diego, CA), with a variable corneal compensator (VCC) to achieve individualized corneal compensation. Clinical application of this device in glaucoma detection is also demonstrated.
Arno Ledebuhr, Joseph Kordas, Isabella Lewis, Michael Richardson, George Cameron, W. Travis White, Douglas Dobie, Wesley Strubhar, Thomas Tassinari, Douglas Sawyer, Michael Shannon, Lyn Pleasance, Albert Lieber, Peter Trost, David Doll, Michael Grote
Lawrence Livermore National Laboratory developed a space-qualified high resolution (HiRes) imaging LIDAR (light detection and ranging) system for use on the DoD Clementine mission. The Clementine mission provided more than 1.7 million images of the moon, earth, and stars, including the first ever complete systematic surface mapping of the moon from the ultra-violet to near-infrared spectral regions. This article describes the Clementine HiRes/LIDAR system, discusses design goals and preliminary estimates of on-orbit performance, and summarizes lessons learned in building and using the sensor. The LIDAR receiver system consists of a HiRes imaging channel which incorporates an intensified multi-spectral visible camera combined with a laser ranging channel which uses an avalanche photo-diode for laser pulse detection and timing. The receiver was bore sighted to a lightweight McDonnell-Douglas diode-pumped Nd:YAG laser transmitter that emitted 1.06 micrometer wavelength pulses of 200 mJ/pulse and 10 ns pulse-width. The LIDAR receiver uses a common F/9.5 Cassegrain telescope assembly. The optical path of the telescope is split using a color-separating beamsplitter. The imaging channel incorporates a filter wheel assembly which spectrally selects the light which is imaged onto a custom 12 mm gated image intensifier fiber-optically coupled into a 384 multiplied by 276 pixel frame transfer CCD FPA. The image intensifier was spectrally sensitive over the 0.4 to 0.8 micrometer wavelength region. The six-position filter wheel contained 4 narrow spectral filters, one broadband and one blocking filter. At periselene (400 km) the HiRes/LIDAR imaged a 2.8 km swath width at 20-meter resolution. The LIDAR function detected differential signal return with a 40-meter range accuracy, with a maximum range capability of 640 km, limited by the bit counter in the range return counting clock. The imagery from the HiRes is most useful for smaller scale topography studies, while the LIDAR data is used for global terrain and inferred gravity maps.
A 12 mm active diameter proximity focused MCP image intensifier tube has been developed having a typical limiting resolution of 45 lp/mm, and a luminous gain of 1E4 fL/fc at 960 V, and a mass of 24 g. In produces about the same number of pixels in its active area as an 18 mm active diameter image tube having a limiting resolution of 32 lp/mm and a mass of 51 g. Its equivalent background input at 23 degree(s)C is essentially the same as an 18 mm tube; i.e., 2E-11 lm/cm2. This 12 mm tube is well suited for use in small and lightweight low light level direct-view systems and TV cameras.
We show that global and local characteristic features of thermal images undergo considerable diurnal changes. In particular, the standard deviation of the gray-level distribution of thermal images increases with the intensity of the solar flux and the diversity of the microtopography, while the spatial correlation length decreases under the same conditions.
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